drm/nouveau/fifo: merge mmu fault handlers together

After updating GF100 implementation from the GK104/TU102 ones, and using
the new runlist/engine topology info, all three handlers become (almost)
identical.

- there's a temporary kludge to call through to the HW-specific recovery
- engine fault mapping info determined at load time, not on every fault

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>